Superpave TM Mix Design Marshall Mix Design 1. Select suitable - PowerPoint PPT Presentation

Superpave TM Mix Design

Marshall Mix Design 1. Select suitable aggregates 2. Select a suitable asphalt binder 3. Select appropriate mixing and compaction temps 4. Select a suitable aggregate structure 5. Mix and compact samples in the lab 6. Analyze mix volumetrics (air voids, etc.) 7. Select the optimum asphalt content 8. Evaluate moisture susceptibility CIVL 3137 2

Superpave Mix Design 1. Select suitable aggregates 2. Select a suitable asphalt binder 3. Select appropriate mixing and compaction temps 4. Select a suitable aggregate structure 5. Mix and compact samples in the lab 6. Analyze mix volumetrics (air voids, etc.) 7. Select the optimum asphalt content 8. Evaluate moisture susceptibility CIVL 3137 3

Superpave Specimens SUPERPAVE Marshall 6" 4" 4700 g 1200 g Aggregate Aggregate CIVL 3137 4

Why 4700‐g Specimens? • The larger specimens better accommodate larger NMAS mixes (up to 1½ inches). Marshall specimens 2½ inches high can be dominated by a single large aggregate particle. 2.5" 4.5" 4.0" 6" CIVL 3137 5

Gyratory Compactor CIVL 3137 6

Gyratory Compaction P = 600 kPa  = 1.25º 30 rpm CIVL 3137 7

Why Gyratory Compaction? • Gyratory compaction produces a kneading motion that better replicates what happens beneath the rollers during compaction on the road surface.  = 1.25º CIVL 3137 8

Superpave Mix Design Approach • Select suitable materials and determine the proper mixing and compacting temperatures. • Determine the best aggregate blend from among several trial blends using specimens compacted at one trial asphalt content. • Estimate the correct asphalt content for the best blend using the results from that one trial. • Determine the optimum asphalt content using specimens compacted at four different asphalt contents around the estimate.

1. Select suitable aggregates Source: NCEES FE Supplied Reference Handbook CIVL 3137 10

2. Select a suitable asphalt binder PG70‐22 PG64‐16 ‐28 ‐22 ‐16 ‐10 ‐4 46 52 58 64 70 76 28 34 40 Lowest Annual Highest Annual 1‐day Pavement 7‐day avg. Pavement Temperature Temperature CIVL 3137 11

3. Determine relevant temperatures Peanut Butter Ketchup Chocolate Syrup Honey AASHTO T-245 MARSHALL COMPACTING TEMP. RANGE (280 +/- 30 cSt) Tomato Juice AASHTO T-245 MARSHALL MIXING TEMP. RANGE (170 +/- 20 cSt) Vegetable Oil CIVL 3137 12

4. Create several aggregate blends Blend 1 Blend 2 Blend 3 CIVL 3137 13

5. Select a Trial Binder Content NMAS Aggregate Relative Density and Absorption (mm) 2.65 / 0.8% 2.65 / 1.6% 2.70 / 0.8% 2.70 / 1.6% 9.5 8.3 8.9 8.1 8.7 12.5 5.0 5.6 4.9 5.5 19 4.4 5.0 4.3 5.0 25 4.1 4.7 4.0 4.6 CIVL 3137 14

A Question to Ponder • Why does the trial binder content drop with increasing NMAS? NMAS Aggregate Relative Density and Absorption (mm) 2.65 / 0.8% 2.65 / 1.6% 2.70 / 0.8% 2.70 / 1.6% 9.5 8.3 8.9 8.1 8.7 12.5 5.0 5.6 4.9 5.5 19 4.4 5.0 4.3 5.0 25 4.1 4.7 4.0 4.6 CIVL 3137 15

Effect of NMAS on Surface Area effective asphalt volume  aggregate surface area 10" surface area = 11 ft 2 surface area = 22 ft 2 CIVL 3137 16

Another Question to Ponder • Why does the trial asphalt content increase with increasing aggregate absorption? NMAS Aggregate Relative Density and Absorption (mm) 2.65 / 0.8% 2.65 / 1.6% 2.70 / 0.8% 2.70 / 1.6% 9.5 8.3 8.9 8.1 8.7 12.5 5.0 5.6 4.9 5.5 19 4.4 5.0 4.3 5.0 25 4.1 4.7 4.0 4.6 CIVL 3137 17

Mix Volumetrics absorbed asphalt volume  aggregate absorption Absorbed Aggregate Asphalt Particle (M BA ,V BA ) (M G ,V G ) Effective Water Asphalt Permeable (M BE ,V BE ) Voids CIVL 3137 18

A Final Question to Ponder • Why does the trial asphalt content decrease with increasing aggregate relative density? NMAS Aggregate Relative Density and Absorption (mm) 2.65 / 0.8% 2.65 / 1.6% 2.70 / 0.8% 2.70 / 1.6% 9.5 8.3 8.9 8.1 8.7 12.5 5.0 5.6 4.9 5.5 19 4.4 5.0 4.3 5.0 25 4.1 4.7 4.0 4.6 CIVL 3137 19

Binder Content Assume two 2-cm-diameter aggregate spheres each with a 0.05-cm-thick asphalt cement coating G s = 2.65 G s = 2.70 m ������� � 1.03 0.9970 g 4 3 π 1.05 cm � � 1.00 cm � � 0.658 g cm � CIVL 3137 20

Binder Content m ��������� � 2.65 0.9970 g 4 3 π 1 cm � � 11.07 g cm � G s = 2.65 m ������� 0.658 P � � � 0.658 � 11.07 � 0.056 � 5.6% m ������� � m ��� CIVL 3137 21

Binder Content m ��������� � 2.70 0.9970 g 4 3 π 1 cm � � 11.28 g cm � G s = 2.70 m ������� 0.658 P � � � 0.658 � 11.28 � 0.055 � 5.5% m ������� � m ��� CIVL 3137 22

6. Select the compaction effort N = number of revolutions in the gyratory compactor < 0.3 0.3 to < 3 3 to < 30 30 + Source: ASTM D6925 ‐ 06 CIVL 3137 23

As the number of gyrations increases, the height of the specimen decreases, so the more gyrations the denser the specimen. This is the same idea behind using more blows per side in the Marshall specimen. 7 1 7 10 75 100 115 CIVL 3137 24

For a given traffic level, we want to know the specimen density after N ini , N des , and N max gyrations. 7 1 N ini 10 N des 100 N max CIVL 3137 25

Superpave Compaction Levels • N initial is used to gage how well the asphalt mix will compact during construction. If it compacts too quickly (the air voids are too low) the mix may be tender during construction and unstable when subjected to traffic. • N design is the number of gyrations required to produce a sample with the same density as that expected in the field after being subjected to further compaction due to traffic. The asphalt mix should have 4% air voids at this density. • N max is the number of gyrations required to produce a sample with greater density than is expected in the field after many years of traffic. If the mix compacts too much (the air voids are too low), it could bleed. CIVL 3137 26

Compaction Requirements N = number of revolutions in the gyratory compactor  11%  2% AIR VOIDS (VTM) 4% CIVL 3137 27

Compaction Requirements N = number of revolutions in the gyratory compactor Source: NCEES FE Supplied Reference Handbook CIVL 3137 29

Initial Trial • Compact two specimens (4700 g of aggregate each) to N des gyrations. • Determine the mix volumetrics (VTM, VMA, VFA). • Estimate the asphalt content that will produce a mix with exactly 4% air voids at N des gyrations. • Estimate VMA, VFA and %G mm @N ini for a specimen with exactly 4% air voids. • If the VMA, VFA and %G mm @N ini requirements are met, this is a suitable aggregate blend. CIVL 3137 30

Assume 2 million ESALs for the sake of this example N ini = 7, N des = 75, N max = 115 N des 1 1 7 10 10 75 100 100 115 115 CIVL 3137 31

Mix Volumetrics (Taken from The Asphalt Institute Manual ES‐1, Second Edition) Weigh in Air Weigh in Water CIVL 3137 32

Calculate G mb @ N des W  in air G @ N mb des  W W SSD in water CIVL 3137 33

Calculate %G mm at N ini    G @ N H   %G @ N mb des des 100%    mm ini G H    mm ini CIVL 3137 34

Assume 2 million ESALs for the sake of this example N ini = 7, N des = 75, N max = 115 (N ini , H ini ) (N des , H des ) 1 1 7 10 10 75 100 100 115 115 CIVL 3137 35

Assume G mm = 2.403 at the trial binder content Assume G mb = 2.369 after N des = 75 gyrations ( 7, 125.8 ) ( 75, 111.5 ) 1 1 7 10 10 75 100 100 115 115 CIVL 3137 36

Calculate %G mm at N ini    G @ N H   %G @ N mb des des 100%    mm ini G H    mm ini    2.369 111.5    %G @ N 100% 87.3%    mm ini  2.403  125.8  CIVL 3137 37

Voids in Total Mix (Air Voids)   G @ N    mb des VTM 1 100%   G   mm G mb = bulk specific gravity of compacted mixture D 2726 ‐ Bulk Specific Gravity and Density of Compacted Bituminous Mixtures G mm = maximum specific gravity of the mixture D 2041 ‐ Theoretical Maximum Specific Gravity and Density of Bituminous Paving Mixtures CIVL 3137 38

Voids in Mineral Aggregate      G @ N 1 P    mb des b VMA 1 100%   G   sb G mb = bulk specific gravity of compacted mixture G sb = bulk specific gravity of the aggregate blend P b = asphalt binder content of mixture CIVL 3137 39

Voids Filled with Asphalt   VTM    VFA 1 100%    VMA  VFA is the percentage of the available space between the aggregate particles (the VMA) that is occupied by asphalt binder rather than by air voids. CIVL 3137 40

Estimate P b @ 4% Air Voids      P @4% P 0.4 4% VTM b b CIVL 3137 41

Marshall Mix Design 6 5 Air Voids (%) 4 1 0.4 3 2 1 3.5 4.0 4.5 5.0 5.5 6.0 6.5 Asphalt Content (%) CIVL 3137 42